Purification system for wastewater coming from fruit and vegetable processing plants and phytosanitary treatments in the field

ABSTRACT

Said equipment include a tank-filter ( 1, 15 ) in which a pretreatment stage is carried out. The tank ( 1 ) is a decanter to which a flocculant that is uniformly mixed with an agitator ( 3 ) can be added. The sludge is removed by delivering it to a filter bag ( 5 ). The permeates are then fed to a collecting tank ( 6 ) and pumped to the same tank ( 7 ) receiving the clarified waters. The permeates are then decanted from said tank ( 7 ) through a safety filter ( 8 ) to a battery of activated carbon columns ( 9 ) where they arm purified by adsorption until the established threshold values have been reached. In another embodiment, the reservoir-filter ( 15 ) is a polypropylene bag filter with diatomaceous earth, wherein the liquid passes directly to the decanting tank and is then pumped to the battery of activated carbon columns ( 9 ).

OBJECT OF THE INVENTION

This invention, as stated in the heading to this descriptive report,concerns a purification system for wastewater coming from fruit andvegetable processing plants and phytosanitary treatment in the field,with which notable relevant and advantageous characteristics arecontributed compared to present conventional purification systems.

The wastewater from chemical products generated in fruit and vegetableprocessing plants is purified in the different systems of applicationthat are used: drenchers (pallet dousers), fungicide applicators, waxapplicators, treatment lines and treatment pools, etc., along with thepurification of waste liquid left over from phytosanitary treatmentscarried out in the field.

BACKGROUND OF THE INVENTION

For purification of water contaminated with pesticides, a treatmentsequence is currently followed of: conventional filtration—activatedcarbon—biological degradation, as considered in the decontaminationsystem of invention patent with publication number ES2050909 referringto the detoxification of solutions that could contain toxic substancessuch as pesticide residues.

The system consists of a tank where the liquid is collected, fitted witha basket made of a grating with a hole size of 0.8 mm. The tank has anair inlet for the introduction of compressed air that is mixed with theliquid, thereby improving the degradation of toxic materials in theliquid.

The toxicity level of the water in the tank is established so that,depending on this level, the water is transferred to the appropriatedecontamination subsystems.

With a high level of toxicity, the water is conducted to a retainingtank, fed with a constant source of compressed air.

The treated liquid passes through an earth bed reactor. The reactorincludes a layer of earth on a series of permeable concrete blocks. Theliquid is applied to the upper part of the layer of earth by means of anetwork of conventional drip irrigation pipes. The earth bed reactorcontains microorganisms that utilise the organic materials employed asthe pesticide as a source of nutrients.

The liquid is diverted from the earth filter to an activated carbonfilter. This filter can include a layer of alumina with potassiumpermanganate for oxidising toxic materials.

The final phase of the decontamination system is a settling basin, i.e.,an open permeable pool. This basin does not just eliminate a substantialpart of the water by evaporation, it also improves the quality of thewater by eliminating traces of pesticides. The basin is stocked withspecies of animals and plants for the additional degradation of theorganic material contained in the water.

If wished, a conventional ozonisation system can be included in thesystem for the introduction of ozone in the rotation tank.

Another system that is known has the treatment sequence: filtration bedswith carbon—degradation with specific microorganisms. This method andsystem for treatment of water is considered in invention patent withpublication number WO 94/29224. It considers a system for thepurification of water with a high content of organic components, such aswaste from agricultural chemicals, and a low DBO.

A porous material is used as a filtration medium, carbon, on which isplaced a substrate of specific microorganism (from the Pseudomonasgroup). The water enters into contact with these microorganisms underaerobic conditions.

The system consists of five tanks in series, through which thewastewater is made the flow.

Following a treatment sequence of: activated carbon—filtration, we canmention the utility model number 9301506 referring to a wastewaterpurifier consisting of a vat or trough provided with a stirrer and atank that links to it underneath via an intermediate bypass valve.Contaminated liquid reaches the vat from the fruit and vegetabletreatment zone by means of a pipe, driven by a pump in such a way thatthe contaminated liquid contained in the trough along with a quantity ofactivated carbon is removed by a stirrer.

When the stirrer is stopped, the bypass valve is opened and thecontaminated elements adhered to the carbon fall by means of settlementdown to the lower tank, from where they are extracted.

There also exist other filters and a filtration column for totallycleaning the content of the vat of any impurities. The liquid is made topass through filters in such a way that, by means of closing certainstopcocks before and after an impulsion pump and opening others, thecirculation of the fluid from the fruit and vegetable treatment zonetowards the vat is prevented, while on the other hand, the circulationof the fluid coming from the vat via the filter circuit is facilitated.

Patent of invention with publication number 0447923A1, referring to apolymer adsorption system, reports an effective filtration medium foroils and greases, liquid hydrocarbon, sterols, organic pesticides andother inert liquid compounds with organic bonds and their mixtures.

The filtration medium consists of polyvinyl acetate, whose particleshave a porous structure. The polyvinyl acetate comes in sheet form, inparticular constructed in the form of a sandwich containing particles ofpolyvinyl butyral, and there is also polyvinyl acetate in form ofmulti-chamber structures.

Using a treatment sequence of: biological treatment with specificstrains, mention can be made of invention patent ES2095193 referring tothe use of bacterial strains of the Pseudomonas genera PCH3 and GCH1 forthe bio-restoration of soils and purification of water contaminated withacetamide-based herbicides. This system is characterised by using atleast one of the Pseudomonas strains PCH3 and GCH1 for thebio-transformation of water contaminated with herbicides. For this, thenecessary nutrients have to be added in order to achieve optimisation ofthe bio-transformation. The water has to be inoculated for treating in aculture with at least one of the microorganisms mentioned above, whichmust be immobilised on a solid support of a ceramic, synthetic ororganic nature. The immobilised microorganism is added as a bio-catalystto a bio-reactor, with the conditions being regulated in order tooptimise the transformation process of the contaminant compounds.

With a treatment sequence: filtration ultraviolet, invention patentES2027366 can be mentioned, which discusses an apparatus for watertreatment. The apparatus is designed for the purification of drinkingwater and contains a system for purifying toxic compounds; it is capableof retaining trace quantities.

This apparatus consists of a head with an opening for the entrance ofwater and another for the outlet, and a set of fitted parts that includefiltration means and radiation means.

The filtration means can consist of mechanical fibres and/or chemicaladsorption material, and is preferably of the activated carbon type withgranular transverse section.

The internal diameter of the filtration means is somewhat greater thanthe external diameter of the irradiation means. The irradiation meansincludes an ultraviolet lamp, with or without ozone.

Also using a treatment sequence: (ozone)—ultraviolet—activated carbon,mention can be made of the invention patent WO94/25401, concerning awater purification unit. This system is designed for the purification ofdrinking water and contains a retaining system for toxic compoundsprepared for retaining traces quantities. The water to be purified flowsunder a powerful source of ultraviolet radiation and then passes throughan activated carbon filter fitted on the ultraviolet source. Theeffluent from the filter is again passed through the ultravioletradiation source. This source eliminates the microorganisms present andthe filter retains particles and other compounds.

An ozone generator can be incorporated into the water inlet in order toboost the destruction of microorganisms present and oxidise theundesirable components of the water.

DESCRIPTION OF THE INVENTION

In general terms, the purification system for wastewater coming fromfruit and vegetable processing plants and phytosanitary treatment in thefield, constituting the object of the invention, basically includes thefollowing elements:

First of all, it has a settling tank, of truncated conical shape andmanufactured in polyester reinforced with fiberglass, with anapproximate capacity of 500 1. This tank will contain two or moreoutlets at different heights for the settling, one of which will bearranged so as to start at the conical base and the other at a higherlevel, more specifically at 50% of the height of the cylindrical part ofthat tank. It has a flocculent dosing system and a stirrer for producinga good mix. A filtration system for the sludge is provided at the outletfrom the tank, and the sludge then passes to a filtering bag ofapproximately 820 mm in length and 180 mm in diameter, manufactured insingle-filament nylon with a mesh-size of 60 to 75 microns. The productfiltered in the bag is then passed to a collection tank of approximately50 1 and from here it is pumped to an intermediate tank of dimensionssimilar to the one for settling.

From the intermediate tank, the filtered product passes to aself-cleaning ring filter, of mesh-size 75 microns, and then throughsome activated carbon columns, normally one to three in number, of theorder of 300 1 in volume and containing approximately 100 kg of carbon.They are manufactured in polystyrene with an exterior reinforcement offibreglass and epoxy resin.

There is a system of warning lights for indicating when the activatedcarbon has become exhausted, and also the necessary pumps and valves forthe facility.

The wastewater is pumped from the tanks containing the drenchers usingconventional pumps.

Sometimes, at the outlet from the array of activated carbon columns, anultraviolet lamp is incorporated in order to guarantee a greater degreeof purification.

The system includes a reverse-wash mechanism permitting a greater yieldto be obtained from the activated carbon columns.

In order to facilitate an understanding of the invention, and forming anintegral part of this descriptive report, a sheet of plans is attachedcontaining a single figure in which, by way of illustration and not tobe regarded as restrictive, the following is represented:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1.—This is a diagram of the functioning of the purification systemfor wastewater coming from fruit and vegetable processing plants andphytosanitary treatment in the field, in accordance with the invention.

FIG. 2.—This is another diagrammatic view, similar to FIG. 1,incorporating an ultraviolet lamp.

FIG. 3.—Samples of an installation for carrying out the purificationprocess, including a pressure filter with filtering bags prepared with apre-layer of diatomaceous earth.

FIG. 4.—This is a perspective view of the rotating support carrying theactivated carbon bottles.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

Referring to the numbering system adopted in FIG. 1, we can see how thepurification system for wastewater coming from fruit and vegetableprocessing plants and phytosanitary treatment in the field that theinvention proposes includes a settling system for the wastewater comingfrom the fruit washing drenchers. Its function is to separate thesuspended solids that the wastewater contains and is composed of asettling tank 1 where the wastewater arrives and where flocculent can beadded by means of the flocculation system 2, with mixing by means of astirrer 3. Following the decanting, the sludge is extracted via thelower part of the tank and the clarified water is transferred to theintermediate tank 7.

The approximate efficiencies in the decanting process using flocculationare:

Suspended solids: 50%

DQO: 20%

Imazalil: 20%

Thiabendazol: 80%

It also includes a sludge treatment system in which the sludge isextracted by gravity from the bottom of the settling tank and arrives atthe filtering bag 5, where it is retained and part of the watercontained in the sludge is filtered through it. The filtering bag 5 isarranged in a vertical position inside a metal frame 4 which acts as asecuring for it and as a collector for the water passing through it onits way to the reception tank 6. This water is pumped from the tank 6 toan intermediate tank 7, where it is combined with the clarified water.The reception tank 6 and the intermediate tank 7 may comprise a stirrerfor uniformly mixing the clarified water. The drying of the sludgeachieved by means of the filtering bag system is around 50%.

The clarified water and the water from the filtering bag, collected inthe intermediate tank 7, are pumped via the ring filter 8. This filteracts as a safety filter for the columns of activated carbon, retainingany remaining solids left in the water.

The system also includes the columns of activated carbon, three of themin the examples shown in the diagram. After passing through the safetyfilter 8, the clarified water arrives at the columns of activated carbon9, where it is purified by adsorption, with toxic substances beingremoved down to the threshold values determined by legislation. Thewarning indicator light 10 indicates when the first column of activatedcarbon 9 has become exhausted and needs replacing.

The reference 11 refers to the necessary pumps and valves.

The approximate efficiencies in the columns of carbon are:

Suspended solids: 90%

DQO: 85%

Imazalil: 100%

Thiabendazol: 100%

The ecotoxicity values of the purified water are below 2 U.T.

In the diagram, the settling system for the final fall from thedrenchers is referenced with A, and is accessed by the loading mouth ofthe settling tank 1, as shown by the arrow. In the diagram of FIG. 1,the block of columns of activated carbon 9 is referenced with B. Theblock referenced with C corresponds to the sludge treatment system.

The arrows appearing in the diagram indicate the route followed throughthe installation by the product being purified. The treated water isobtained at the outlet from the block B of columns of activated carbon9.

FIG. 2 is a diagram of an installation that includes an ultraviolet lamp13, which guarantees a greater degree of purification, the product beingcollected in tank 12, from where it exits towards the drain.

A description is now going to be given of the installation in which thepurification process has been carried out, with special reference toFIG. 3, where another manner of carrying out the invention isconsidered.

The dimensioning of the components of the system has been determined fora volume of trencher liquid to be purified of 460 l/h, since the systemhas to be dimensioned for different flows and loads of contaminants.

In order to commence the purification process, about 40 1 of water areintroduced into tank 6 (which has a capacity of around 500 1; theintroduction can be done automatically or manually) and it is connectedto the stirrer 3 and the pump 11 a in closed circuit via the bag filter15 and the stopcock 14 a. After that, some diatomaceous earth is thenadded little by little and the circulation is kept up for at least 5minutes.

Once the circulation time has ended, the filtering bags 5 of thispressure filter 15 are prepared with a preload of diatomaceous earth. Atthat moment the electrovalve 14 a is closed and number 14 b is opened,which causes the pumps 11 a to suck the liquid to be purified andintroduce it into the tank 6 with the solids being filtered down to aparticle size of less than 50 microns.

In this pressure filter 15, a pretreatment or conditioning stage of thedischarge takes place. In a second stage, the final treatment orreduction of the contaminant load is produced.

In this first pretreatment stage, what is sought is to reduce the loadof solids present in the water coming from the drencher, and to proceedto an initial reduction of the contaminating load. For this purpose, apolypropylene bag filter (of no more than 50 microns) is provided forretaining all solids larger than this pore size. To help the filtrationsystem diatomaceous earth is included, forming a pre-layer on the insideof the polypropylene bags, taking advantage of the selectivepermeability of this earth and the power it has to adsorb oils.

The objective is multiple:

To help in the filtering, improving it by preventing rapid clogging.

To retain the small percentage of oil from the preparations.

To protect the walls of the bag and thereby extend their life.

The final result of the combination of ball/diatomaceous earth is:

Very high reduction of sedimentable solids.

High reduction of suspended solids.

Reduction of the pesticide load.

Reduction of oils present.

In the case of proceeding to the purification of water from processinglines, these would first be stored in a retaining tank 16 of a suitablesize so that the water can be purified at the necessary speed.

Once the liquids have been filtered in the tank 6, the pump 11 b isstarted up, driving the liquids through three bottles 9 of activatedcarbon making up the array of columns 9, with each of them having avolume of the order of 316 1. A minimum permanency of two hours for theliquid inside the bottles 9 of activated carbon must be guaranteed. Forthis, there is a litre counter with an electronic output connected to anelectrical automatism that prevents the pump from continuing to drivethe liquid until the liquid that is inside the bottles 9 has remainedthere for at least two hours. These control means provide that mixedclarified water is retained in each carbon column 9 for at least twohours. Moreover, this volumetric counter will also be in charge ofwarning that the activated carbon in the first bottle 9 is becomingexhausted and needs to be replaced. A telephone warning device can beconnected so that the supplier company can proceed to carry out thechange. The system has been designed so that a fourth bottle ofactivated carbon can be incorporated, as shown in FIG. 4. In this way,the third bottle would easily be able to be replaced by the spare one,with this third bottle taking over the position of the second one, whichwould in turn occupy the first position once the clogged up bottle hadbeen removed. These four bottles 9 are located on a rotating plate 17,this entire process of permutation being carried out by means of asimple motorized or manual rotation through 90°, as can be easilydeduced from observing the figure.

Control over the system is done by means of a programmable automationconnected to a touch-sensitive screen enabling the user to programme allthe operational parameters of the system, with the records of flows andconsumptions, warnings of replacements, etc., and permitting connectionto a personal computer for greater versatility in its handling. Thiscomputer can in turn be connected to another remote terminal by modem,permitting remote control.

The first filtering bottle 9 incorporates a reverse-wash valve 18permitting this process to be carried out in the event of the activatedcarbon in the first bottle 9 becoming compacted, since this bottle isthe one that suffers the greatest contaminant load. This process can becarried out automatically once the differential pressure between theinlet and the outlet exceeds a defined value. The water from thereverse-washing is returned to the tank 6 for being treated as if itwere an ordinary part of the liquid for purifying.

Once the liquid exits from the bottles 9 of activated carbon, it couldoptionally be treated by means of ultraviolet lamps 13 and/or anozoniser 19, before being discharged.

The reference 20 in FIG. 3 refers to a flow meter.

What is claimed is:
 1. A purification system for wastewater fromfruit-and vegetable-processing plants and from phytosanitary treatments,the system comprising: a filter tank where a pretreatment step iscarried out; a tank for collecting clarified water resulting from thepretreatment step, said tank comprising a stirrer for uniformly mixingthe clarified water; pumping means for pumping mixed clarified waterfrom said tank to a first activated carbon column of an array ofactivated carbon columns being prepared for purifying the mixedclarified water by adsorption up to established threshold values; saidfirst activated carbon column being connected by an outlet to an inletof a subsequent activated carbon column, each further subsequentactivated carbon column being connected by its inlet to the outlet ofthe preceding activated carbon column; and automatic control means forproviding that mixed clarified water is retained in the carbon columnsfor at least two hours.
 2. A purification system according to claim 1,wherein the tank-filter is a settling tank with at least two outlets forthe clarified water, to which flocculent can be added, the sludge beingextracted by gravity through the lower part thereof and sent to afiltering bag where it is retained, while the clarified water is sent toan intermediate tank, being joined to this the water which passesthrough said filtering bag and is received in a collection tank.
 3. Apurification system according to claim 2, wherein the filtering bag isarranged inside a metal frame which acts as a support for it and as acollector for the water passing through it on its way to the receptiontank.
 4. A purification system according to claim 1, wherein thetank-filter is a polypropylene bag filter that includes diatomaceousearth, with circulation being maintained in closed circuit from the tankcontaining water, the bags being filled with a pre-layer of this earth;a pump sucking the liquid to be purified and which passes through thatfilter to the reception tank, from where it is decanted to the array ofcolumns of activated carbon.
 5. A purification system characterizedaccording to claim 1, wherein at the outlet from the array of columns ofactivated carbon is included an ultraviolet lamp.
 6. A purificationsystem for wastewater coming from fruit and vegetable processing plantsand phytosanitary treatments in the field, according to claim 1, whereinthe array of columns of activated carbon, three in number, is mounted ona rotating plate where there exists a fourth column.